Recently I discovered a funny thing, that tag cloud widgets get mixed up between my blogs, that were the part of the same installation using WordPress 3.0.1 Multisite, and the latest version of WP Widget Cache.

I started to dig a bit deeper, and I found a problem around cache key creating.
For example if you have a tag cloud widget in the first position of the sidebar on many blogs, the first one that shows up, and get cached will be displayed everywhere…

The solution I came up with, is that simply add the domain name of the site into the widget cache key, so it will be totally unique around the site, and the installation as well.